Garnet structure ferrimagnetic material having a saturation magnetisation less than 1000 gauss for microwave applications

ABSTRACT

A garnet structure ferrimagnetic material designed to operate at frequencies of around 2000 Mc/s and below, with very high stability and reduced losses, at high peak power, is provided. The material satisfies the basic molecular formula:

United States Patent [191 Nicolas et al.

[451 May 27,1975

[ GARNET STRUCTURE FERRIMAGNETIC MATERIAL HAVING A SATURATION MAGNETISATION LESS THAN 1000 GAUSS FOR MICROWAVE APPLICATIONS [75] Inventors: Jean Nicolas; Alain Lagrange;

Roland Sroussi, all of Paris, France [73] Assignee: Thomson-CSF, Paris, France [22] Filed: Mar. 30, 1973 [2]] App]. No.: 346,245

[30] Foreign Application Priority Data Mar. 31, 1972 France 72.11633 [56] References Cited UNITED STATES PATENTS 3,479,292 11/1969 Chegwidden et a1. 252/6257 2/1971 West 252/6257 3/1972 Lagrange et al. 252/6257 Primary Examiner-Jack Cooper Attorney, Agent, or Firm-Cushman, Darby & Cushman 5 7] ABSTRACT A garnet structure ferrimagnetic material designed to operate at frequencies of around 2000 Mc/s and below, with very high stability and reduced losses, at high peak power, is provided. The material satisfies the basic molecular formula:

where:

0.5 x 0.8 0 y 0.12 0 z 0.4

It exhibits a saturation magnetisation less than 1000 gauss.

6 Claims, 4 Drawing Figures SHEET PATENTED rm 2 7 915 DC=O,8 5 (qauss) 20,3

GARNET STRUCTURE FERRIMAGNETIC MATERIAL HAVING A SATURATION MAGNETISATION LESS THAN 1000 GAUSS FOR MICROWAVE APPLICATIONS The present invention relates to a ferrimagnetic material of garnet structure, which is particularly suitable for microwave applications in the range extending from some few hundred to some few thousand Mc/s.

Those skilled in the art will be aware of the existence of materials of garnet structure, which are employed in microwave applications. The prototype of these materials is yttrium garnet of the formula Y Fe 0 having a saturation magnetisation of 1750 gauss at ambient temperature, and a gyroresonance line width (measured at Gc/s) of around 50 oersteds. Its dielectric losses (measured at 10 Gc/s) can be very low indeed (tg8 l0 At relatively low frequencies, for example two Gc/s, it is frequently necessary to have materials which possess a small saturation magnetisation, less than 900 gauss for example. To achieve this result, means are known such as the substitution of aluminum or gallium for iron, or of gadolinium for yttrium in the case of yttrium garnet.

The chief characteristics to bear in mind, for a given magnetisation, are, in addition to the dielectric characteristics, the stability of the magnetic moment as a function of temperature and the value of the width of the gyroresonance line. If the magnetic moment is diminished by substitutions of aluminium (or gallium), the temperature stability is severely impaired, but the widths of the resonance lines remain narrow which is an advantage. If the magnetic moment is reduced by gadolinium substitutions, the temperature stability is improved (for a saturation magnetisation ranging between 900 and 1700 gauss) but the width of the gyroresonance line increases which is a drawback.

The invention relates to a material of low saturation magnetisation (less than 1000 gauss) having at one and the same time a high stability as a function of temperature and quite narrow line widths.

Garnet structure ferrimagnetic material in accordance with the invention, has a general chemical composition satisfying the formula:

where:

0 z 0.4 and: e is close to 0 (residual lack of stoichiometry).

This material can be obtained in the following manner: basic materials are chosen (for example iron oxide, yttrium oxide, gadolinium oxide, calcium carbonate, tin oxide and alumina) which have very high purity, especially in the case of yttrium and gadolinium oxides, which should have a purity of better than 99.95%; these materials are weighed and mixed in accordance with the recipe described by the general formula in which, at the start, e is replaced by e, the latter being made equal to 0.035 in the case, described hereinafter, of two successive operations of crushing the material in steel jars utilizing steel balls. In addition, in dosing or measuring out the basic materials, the firing losses of the different oxides are taken into account, that is to say the losses in water and organic materials, incurred during later heat treatments.

The thus dosed mixture is then dried, screened and fired, that is to say heat treated in an oxidising atmosphere at a temperature between 1 150 and 1250 C for a period of half an hour to 2 hours.

The fired product is then crushed in steel jars using steel balls, in a water environment, for 48 hours. It is then dried, screened and mixed with an organic binder such as an aqueous solution of 10% of polyvinyl alcohol. The product thus obtained is screened again to obtain a granulate suitable for introduction into moulds,

where, under properconditions, it can be pressed into shape. This pressing takes place under a pressure of one ton per cm The press-mouldings thus obtained are dried, then treated in an oven at a sintering temperature ranging between l350 and l500 C, in an oxidising atmosphere, for at least 2 hours.

The invention will be better understood and other of its features rendered apparent from a consideration of the ensuing description and the annexed drawings in which:

FIGS. 1 to 4 illustrate, in respect of different values of the parameters x, y and z, in the general formula, the variations in saturation magnetisation as a function of temperature.

Six typical examples are described, each corresponding to a range of values of the parameters.

First example of the material in accordance with the invention y varying from 0 to 0.10.

In addition, manufacture is specified as follows:

stoichiometry error at initial weigh-in:e'=0.0.35;

firing temperature: 1 200 C;

sintering temperature from l415 to 1465' C;

sintering time at optimum temperature of 1430 C:24

hours.

In this fashion, a material having denisty ranging between 5.78 (y=0.10) and 5.87 (y=0), a dielectric constant in the order of 15 at 8.2 Gc/s and a gyromagnetic factor in the order of 2 to 9.5 Gc/s (measured on a 1 mm diameter sphere of the material), is obtained.

Hereinafter, the notations utilised in the tables and graphs are defined:

41rM is the saturation magnetisation in gauss, measured at ambient temperature (in the order of 20 C although this value is not critical because of the high stability of the materials in accordance with the invention);

6' is the dielectric constant in U.E.M.C.G.S.;

tg8 is the tangent of the dielectric loss angle measured at a frequency of 8.2 Gc/s;

g is the gyromagnetic factor;

AH is the width in oersteds of the gyromagnetic resonance line measured at 9.5 Gc/s on a 1 mm diameter sphere;

K and K are the temperature coefficients of the saturation magnetisation 41rM between the following temperatures:

40 C and C for K 0 C and +l00 C for K The experimental results have been summarised in the following table:

TABLE I Sintering temperature 1430" C lELD d 41-rM e tgB 1 g AH K K .l0

lg/cm) (gauss) spin waves measured at a frequency of 9.4 Gc/s when using parallel pumping. The value of AH provides information on the critical field strength at the frequency in question and, consequently, upon the peak power which can be applied. This power is the higher the greater AH is.

FIG. 2, similar to FIG. I, shows in respect of this second example that good stability is achieved in the practical range of application.

Table II listed hereinafter repeats the characteristics set out in table I, an extra column being added for the parameter AH which is in oersteds.

TABLE II x 0.6 2 0.3 7 1 I 417M,- 5 @10 g AH AH 1 .10" 10.10

tgl m (g (0 (0 The first example points out the advantages of the iny varying from 0 to 0.12.

The specific conditions of manufacture are the same as in the first example, except as far as the sintering temperatures (here from 1380 to 1465 C) and the duration of sintering (8 hours at 1400 C), are concerned.

The other sintering temperatures give results which are quite close together; the narrowest AH values obtained are in the order of oersteds for a sintering temperature of 1430C.

Third example of the material in accordance with the invention y varying from 0 to 0.10.

The specific manufacturing conditions are the same as in the second example, except as far as the sintering temperatures (here from l400 to 1485 C).

Thus, a series of materials having densities of 5.89 (y=0.l0) to 5.98 (y=0), a dielectric constant in the order of 15 and a gyromagnetic factor in the order of 2 (measured on a 1 mm sphere), is obtained.

TABLE III x 0.7 2 0.3 y d e tg810 rrM g AH K 10'' K 10 (g/cm) (gauss) (0c) Thus, a series of materials having densities ranging between 5.76 (y=0.04 and y=0.l2) and 5.80 (y=0.l having dielectric constants of the order of 14 to 15 at a frequency of 8.2 Gc/s, and a gyromagnetic factor of 65 2 to 9.5 Gc/s (measured on a 1 mm sphere), is obtained.

To the notations defined in respect of the first example, here AH is added, this being the line width of the Fourth example of the material in accordance with the invention y varying from to 0.06.

The specific conditions of manufacture are the same as in the third example except as far as the sintering temperature is concerned (here from 1400" to 1465 C).

Thus, a series of materials having densities close to 6 (6.07 for y=0.02 and 6.01 for y=0.06), having dielectric constants in the order of 14.5 to 15, and a gyromagnetic factor in .the order of 2 (measured on a 1 mm Sixth example of the material in accordance with the invention In this example, it was sought to improve the qualities of the material by dealing with the initial stoichiometry error (e') defined hereinbefore. For the rest, the parameters x, y and z were maintainedfixed, as also the 15 sphere), 18 obtained. conditions of manufacture.

TABLE 1V .r 0.8 0.3 y (1 4'n'M e tg5l0" g AH K K 10 (g/cm") (gauss) (oe) TABLE V1 1: 0.7 e varing from 0.02 to 0.06 y 0.4 sintering at 1400 C. 2 0.3 e d 41rM e tg810" g AH (g/cm) (gauss) The other sintering temperatures give results very close to these. FIG. 4 illustrates the magnetisation graphs as a function of temperature, for these materials. Extraordinarilygood temperature stability figures are obtained, especially between 0 and 100 C, for the It will be seen that the initial stoichiometry error which gives the minimum dielectric losses, is at around For this value of e, different sintering operations give the material the following values:

materials with y=0.02 and y=0.04 (4'rrM between 550 and 700 gauss approximately). Fifth example of the material in accordance with the invention y varying from 0 to 0.10.

Several sintering operations 'at temperatures ranging between l400 and 1485" C, were carried out. Sintering at 1400 C for 15 hours gave the following results, set out in Table V.

TABLE V x 0.8 2 0.4 y d 41rM e g, AH

( g/cm") gauss) (0c) It will be seen that with a properly chosen stoichiometry and sintering temperature, very low values of dielectric loss tg8l.l0 can be obtained without changing the other characteristics.

The material in accordance with the invention, illustrated in the six examples given hereinbefore, has remarkable characteristis:

small gyroresonance line widths for values of 41'rM ranging between approximately 300 and 900 gauss, and particularly small magnetic moment temperature coefficients (K l.l0), in a wide temperature range.

In addition, these high-gadolinium compounds, as those skilled in the art will be aware, have a good peak power handling capacity (relatively high values of AH in table II for example).

The invention is applicable to various devices utilised in microwave work, especially at relatively low frequencies s 2000 Mc/s) where high temperature stability and good mean and peak microwave power handling capacity, are needed.

What we claim is:

1. Ferrimagnetic polycrystaline garnet structure material having the general formula:

x=().6 z=0.3 0.04 s y s 0.12

4. The material as claimed in claim 1 wherein:

x=0.7 z=0.3 0.02s ys 0.10

5. The material as claimed in claim 1 wherein:

A=0.8 z=0.3 0.02 s Y 0.06

6. The material as claimed in claim 1 wherein:

0.02 s Ys 0.10 

1. FERRIMAGNETIC POLYCRYSTALINE GARNET STRUCTURE MATERIAL HAVING THE GENERAL FORMULA:
 2. The material as claimed in claim 1 wherein: x 0.6 z 0.2 0.02 < or = y < or = 0.10
 3. The material as claimed in claim 1 wherein: x 0.6 z 0.3 0.04 < or = y < or = 0.12
 4. The material as claimed in claim 1 wherein: x 0.7 z 0.3 0.02 < or = y < or = 0.10
 5. The material as claimed in claim 1 wherein: x 0.8 z 0.3 0.02 < or = Y < or = 0.06
 6. The material as claimed in claim 1 wherein: x 0.8 z 0.4 0.02 < or = Y < or = 0.10 